Murine leukemia viruses (MuLV) have been isolated from the wild mice of So. California. These non-acute leukemia viruses belong to the family of type C retroviruses. They do not possess any known oncogene and are unable to transform cells in culture. However, they cause splenic lymphoma in wild, as well as, susceptible inbred mice. These wild mouse MuLVs have many similarities with human T-cell leukemia Virus. As a model for human lymphoma/leukemia, the wild mouse MuLV-induced splenic lymphoma closely resembles childhood acute lymphoblastic leukemia. The overall objective of the present investigation is to develop an anti-retroviral approach which will cause specific cleavage of the viral RNA, inhibiting virus infection in a cultured cell and virus-induced splenic lymphoma in mice. The recent discovery of ribozymes has shown that specific RNA molecules can work as enzymes and degrade target RNA molecules. Of t he various ribozymes, the hammerhead ribozyme catalytic domain appears to be the simplest one, and the catalytic center can be easily incorporated into anti-sense RNA. Specific targeting of a ribozyme against a particular RNA inside the cell, however, appears to pose a major problem. In the proposed study, a hammer-head ribozyme will be designed, synthesized, and targeted against the MuLV RNA by taking advantage of the psi sequence (retroviral RNA packaging signal) of an MuLV-based retroviral vector. It is expected that such a sequence will colocalize the ribozyme and the MuLV genomic RNA in the cytoplasmic micro-environment of the infected cell, aiding trans- cleavage of the viral RNA. Additionally, such a ribozyme construct will also be incorporated in the germline of mice. Protection of the transgenic mice against virus challenge and mild mouse MuLV 10A1-induced lymphomagenesis would thus provide a rational basis for extending this strategy for the treatment of retrovirus-associated human cancer such as T- cell leukemia and retrovirus induced allied diseases like acquired immunodeficiency syndrome (AIDS)